Repeated measures MIXED ANOVA Error

Hello, I am having a horrible time trying to analyse my data. After reading a lot I decided that I need to use a RM Mixed ANOVA. I am trying to find out if production of PGF2a varies between control and three concentrations of LPS and across time (24, 48 and 72h). I have data from 6 different horses.

My data looks like this:

where 1 is control, 2 is lps low concentration, 3 is lps mid concentration and 4 is lps high concentration. each horse has a different number to differentiate them